An IMS is a development direction of future multimedia communication, and is also the most important part of a Next Generation Network (NGN). The IMS is a subsystem supporting an Internet Protocol (IP) multimedia service and proposed by a Third Generation Partnership Project (3GPP), and a remarkable feature of the IMS is that a Session Initial Protocol (SIP) system is adopted and communication is independent of an access way. The IMS may have multiple capacities, such as the capacity of separating multiple multimedia service control functions from a bearing capacity, the capacity of separating a call from a session, the capacity of separating an application from a service, the capacity of separating traffic from a network, and the capacity of converging a mobile network and the Internet.
The IMS provides a new multimedia service form, provides more services for users, and opens up a new income source for operators. Multimedia services of the IMS include a VoIP, Presence, Push-to-Talk over Cellular (PoC), InstantMessage, VideoSharing, content sharing, RichCall and the like. In addition, under an enterprise's fixed environment, the IMS can also provide a service similar to existing fixed switching, for example, by an IPCentrex server, and the IMS can provide a enterprise switchboard service to implement inner-enterprise's short numbers interworking. By an IPConference server, the IMS can provide a conference call service to enable a cell phone, a Personal Computer (PC) and a traditional telephone to dial in the same system, so as to implement a conference call.
In the current industry background, mobile operators, fixed operators, and mobile/fixed mixture operators have the possibility of convergence in roles first. That is, a mobile operator may become a mobile/fixed mixture operator, and a fixed operator may obtain a mobile operating license, and so on. Therefore, all telecom operators urgently need technology to converge a mobile network and a fixed network together. And the IMS exactly has such characteristic. The IMS is independent of a specific bearing type, and may provide a consecutive service of IMS traffic (for example, from voice to multimedia data) for an arbitrary IP channel. The IMS also has an interworking capability with a traditional network, which enables an IMS terminal to implement interworking with a traditional mobile terminal and a traditional fixed terminal.
A converged network will bring users new service experience. No matter what the access network and terminal devices are, users can obtain the same voice and multimedia service in the same way. As such, the compatibility of mobility and individuation is achieved.
Nowadays, many famous Internet service providers have achieved great success by providing a user-to-user communication service, such as MSN, QQ and Skype. The provided services mainly include VoIP, instant messaging, video chat and on the like. Obviously, these applications have a great impact on existing telecom operators' voice and information services. However, at the same time, if these Internet applications are transplanted to a mobile terminal, it is also a new traffic opportunity for telecom operators. And the IMS can provide such technical means. The IMS can provide services, such as VoIP, instant messaging and video chat, which may either replace or interwork with the above Internet services. Therefore, in the face of Internet service providers, telecom operators may have multiple solutions because of the IMS: creating their own brands, competing with the Internet, and implementing the interworking cooperation or choosing competition together with cooperation.
From the point of view of Internet competitions, when users are able to access a Wireless Local Area Network (WLAN) and in a roaming area of high charge (such as international roaming), the users prefer to use VoIP applications (such as Skype and Google Voice) instead of a traditional telephone.
From the point of view of telecom networks, VoIP applications similar to Skype and Google Voice may be provided technically via an IMS, and the IMS may integrate a user number of a non IMS network, provide ways such as Internet Connection Sharing (ICS) or convergence call, thus making it incredibly competitive.
However, there is the requirement of bandwidth, for example, the access to 3G, Long Term Evolution (LTE) or a WLAN. For the data access of 2.5G, its requirement for voice or video cannot be satisfied. In consideration of the case where users are moving, it is required to supply a supplement of 2G voices, such as ICS. At the same time, in the case of daily WLAN access, for example, WLAN access at home or in the office, it is required to configure a strategy for an accessing location (geographic location), such as prohibition of registration, and permission of registration with prohibition of certain applications (such as call).
To burgeoning operators, although an advanced network such as an IMS and a Next Generation Network (NGN) has been deployed, the shortage of number segment resources of a non IMS network leads to the bottleneck of interworking between the advanced network and the non IMS network.